feat(commands): add CLOSE, HIDE, VISUALSTYLES, QUICKCALC, HYPERLINK, XOPEN

Six more standard commands by reusing existing infrastructure:
- CLOSE: close the active tab (Message::TabClose)
- HIDE / VISUALSTYLES: per-viewport render mode (Message::SetRenderMode)
- QUICKCALC / QC: alias the CAL arithmetic evaluator
- HYPERLINK <url>: attach a hyperlink via the PE_URL XData record
- XOPEN: open a selected xref's source file (Message::OpenRecent)

COMMANDS.md updated to 214 done / 15 partial / 33 missing of 262.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/commands/fileops.rs

@@ -137,6 +137,12 @@ impl OpenCADStudio {
                     .push_output(&format!("Visual style: {label}."));
                 return Some(Task::done(Message::SetWireframe(wireframe)));
             }
+            // CLOSE — close the active drawing tab (with the unsaved-changes
+            // prompt the tab-close handler already runs).
+            "CLOSE" => {
+                return Some(Task::done(Message::TabClose(self.active_tab)));
+            }
+
             "EXIT" | "QUIT" => {
                 // Funnel through the OS close path so the unsaved-changes
                 // dialog runs before `iced::exit()`. Falls back to a hard